1. Field of the Invention
The present invention relates to a remote condition monitoring system for monitoring electrical equipment, such as an electric submersible pump (ESP) motor, in for example a downwell or sub-sea environment.
2. Description of Related Art
Systems for monitoring the performance of downhole production or sub-sea equipment would be very useful. Such monitoring systems could extend the lifetime of downhole production equipment, such as ESP motors, by ensuring that their operating parameters stay within safe limits. Unfortunately, there are no systems currently available that are suitable for monitoring the operation of downhole ESP motors. However, some downhole systems do include temperature and pressure sensors, typically based on fibre Bragg grating technology, for monitoring changes in the downwell environment. Because the most common reasons for ESP failures are the poor power factor operation or inadequate start-up procedures leading to significant overheating of the motor windings, it would be desirable to extend downwell monitoring capability to measuring voltage and current on the ESP motor terminals. This would allow a faster response to off-optimal operating conditions of the motor, thereby reducing the cumulative duration of electrical, thermal and mechanical stress on the motor.
Whilst numerous voltage and current sensors are known, many are not suitable for use downwell, primarily because of the extreme conditions of temperature and pressure and the need to send signals over large distances from the downwell equipment to surface stations. This is becoming a more significant problem because as the main offshore reservoirs become depleted, operators are increasingly considering the exploitation of satellite fields within the vicinity using sub-sea ESPs at large step-out distances in the region of or even in excess of 30 km.
The projected use of higher rating ESPs over longer distances has presented designers with a number of potential problems that do not exist to the same degree with schemes in current use. These problems relate to the possibility of cable overvoltage conditions in certain circumstances, the operation of the system at higher nominal voltages and potentially costly maintenance due to the retrieval and replacement of the ESP and lost productivity. It is for these reasons that improved methods of control and the introduction of novel monitoring techniques, tailored to the industry's needs are seen as a necessary enhancement for future ESP schemes.